Spiral Matrix II

注意边界

public class Solution {
    public int[][] generateMatrix(int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(n <= 0)
            return new int[0][];
        int[][] matrix = new int[n][n];
        printCircle(matrix, 0, n, 1);
        return matrix;
    }
    private void printCircle(int[][] matrix, int start, int end, int n)
    {
        if(start >= end)
            return;
        if(end - start == 1){
            matrix[start][start] = n;
            return;
        }
        for(int i = start; i < end - 1; i++)
        {
            matrix[start][i] = n;
            n++;
        }
        for(int i = start; i < end - 1; i++)
        {
            matrix[i][end - 1] = n;
            n++;
        }
        for(int i = end - 1; i > start; i--)
        {
            matrix[end - 1][i] = n;
            n++;
        }
        for(int i = end - 1; i > start; i--)
        {
            matrix[i][start] = n;
            n++;
        }
        printCircle(matrix, start+1, end-1, n);
    }
}